Method of making a shaped polyester article

ABSTRACT

Disclosed is a method of making shaped articles including a continuous polyester phase having dispersed therein microbeads of cellulose acetate which are at least partially bordered by void space, the microbeads of cellulose acetate being present in an amount of about 10-30% by weight based on the weight of said polyester, said void space occupying about 2-50% by volume of said shaped article. Articles made by this method have excellent physical properties, especially optical properties, and are useful in such applications as paper substitutes, for example.

This is a divisional of application Ser. No. 047,821 filed on May 5,1987 now U.S. Pat. No. 4,770,931.

TECHNICAL FIELD

The present invention is directed to shaped articles such as films,sheets, bottles, tubes, fibers and rods having a polyester continuousphase containing cellulose ester microbeads dispersed therein which areat least partially bordered by voids. The articles have uniqueproperties of texture, opaqueness, whiteness in the absence ofcolorants, and generally good physical properties such as tensileproperties.

BACKGROUND OF THE INVENTION

Blends of linear polyesters with other incompatible materials of organicor inorganic nature to form microvoided structures are well-known in theart. U.S. Pat. No. 3,154,461 discloses, for example, the linearpolyester, poly(ethylene terephthalate), blended with, for example,calcium carbonate. U.S. Pat. No. 3,944,699 discloses blends of linearpolyester, preferably poly(ethylene terephthalate) with 3 to 27% oforganic material such as ethylene or propylene polymer. U.S. Pat. No.3,640,944 also discloses the use of poly(ethylene terephthalate) butblended with 8% organic material such as polysulfone orpoly(4-methyl,1-pentene). U.S. Pat. No. 4,377,616 discloses a blend ofpolypropylene to serve as the matrix with a small percentage of anotherand incompatible organic material, nylon, to initiate microvoiding inthe polypropylene matrix. U.K. Patent Specification 1,563,591 discloseslinear polyester polymers, and particularly poly(ethyleneterephthalate), for making an opaque thermoplastic film support in whichhave been blended finely divided particles of barium sulfate togetherwith a void-promoting polyolefin, such as polyethylene, polypropyleneand poly-4-methyl-1-pentene.

The above-mentioned patents show that it is known to use incompatibleblends to form films having paper-like characteristics after such blendshave been extruded into films and the films have been quenched,biaxially oriented and heat set. The minor component of the blend, dueto its incompatibility with the major component of the blend, upon meltextrusion into film forms generally spherical particles each of whichinitiates a microvoid in the resulting matrix formed by the majorcomponent. The melting points of the void initiating particles, in theuse of organic materials, should be above the glass transitiontemperature of the major component of the blend and particularly at thetemperature of biaxial orientation.

As indicated in U.S. Pat. No. 4,377,616, spherical particles initiatevoids of unusual regularity and orientation in a stratified relationshipthroughout the matrix material after biaxial orientation of the extrudedfilm. Each void tends to be of like shape, not necessarily of like sizesince the size depends upon the size of the particle.

Ideally, each void assumes a shape defined by two opposed and edgecontacting concave disks. In other words, the voids tend to have alens-like or biconvex shape. The voids are oriented so that the twomajor dimensions are aligned in correspondence with the direction oforientation of the film structure. One major dimension is aligned withmachine direction orientation, a second major dimension is aligned withthe transverse direction orientation, and a minor dimensionapproximately corresponds to the cross-section dimension of thevoid-initiating particle.

The voids generally tend to be closed cells, and thus there is virtuallyno path open from one side of a biaxially oriented film to the otherside through which liquid or gas can traverse.

Upon biaxial orientation of the resulting extruded film, the filmbecomes white and opaque, the opacity resulting from light beingscattered from the walls of the microvoids. The transmission of lightthrough the film becomes lessened with increased number and withincreased size of the microvoids relative to the size of a particlewithin each microvoid.

Also, upon biaxial orientation, a matte finish on the surface of thefilm results, as discussed in U.S. Pat. No. 3,154,461. The particlesadjacent the surfaces of the film tend to be incompressible and thusform projections without rupturing the surface. Such matte finishesenable the film to be written upon with pencil or with inks, crayons,and the like.

Although the films discussed so far generally white and opaque, suitabledyes may be used either in what will become the matrix polymer or in thevoid initiating particles. U.S. Pat. No. 4,377,616 points out thatinteresting effects can be achieved by the use of spheres of differentcolors or by the use of spheres of different color absorption orreflectance. The light scattered in a particular void may additionallyeither be absorbed or reflected by the void initiating sphere and aseparate color contribution is made to the light scattering in eachvoid.

U.S. Pat. No. 4,377,616 discloses that preferred particle size of a voidinitiating sphere may be about 0.1 to about 10 microns, and thatpreferred particle size range from about 0.75 to about 2 microns. U.S.Pat. No. 3,154,461 specifies that a range of sizes may be approximately0.3 micron to approximately 20 microns, and that when calcium carbonateis used, its size may range from 1 to 5 microns.

U.S. Pat. No. 3.944,699, for example, indicates that the linearpolyester component of the film may comprise any thermoplastic filmforming polyester which may be produced by condensing one or moredicarboxylic acids or a lower alkyl diester thereof, such asterephthalic acid, isophthalic acid, 2,5-,2,6- or 2,7-naphthalenedicarboxylic acid, succinic acid, sebaric acid, adipic acid, azelaicacid, bibenzoic acid, and hexahydroterephthalic acid, or bis-p-carboxyphenoxy ethane, with one or more glycols. Such glycols may includeethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, and1,4-cyclohexanedimethanol. Also, a copolyester of any of theabove-indicated materials may be used. The preferred polyester ispoly(ethylene terephthalate).

U.S. Pat. No. 3,944,699 also indicates that the extrusion quenching andstretching of the film may be effected by any process which is known inthe art for producing oriented film, such as by a flat film process or abubble or tubular process. The flat film process involves extruding theblend through a slit dye and rapidly quenching the extruded web upon achilled casting drum so that the polyester component of the film isquenched into the amorphous state. The quenched film is then biaxiallyoriented by stretching in mutually perpendicular directions at atemperature above the glass transition temperature of the polyester. Thefilm may be stretched in one direction and then in a second direction ormay be simultaneously stretched in both directions. After the film hasbeen stretched it is heat set by heating to a temperature sufficient tocrystallize the polyester while restraining the film against retractionin both directions of stretching.

Paper is essentially a non-woven sheet of more or less randomly arrayedfibers. The key properties of these structures are opacity, texture,strength, and stability. Obviously, fiber technology evolvedsynergistically with paper, and today we have a variety of syntheticfibers and synthetic papers. In both areas, however, the syntheticmaterials have never quite matched the cellulose-based natural polymers,like cotton for fibers and cellulose pulps for papers. On the otherhand, the natural polymers are generally weaker and less stable. Aserious problem, for example, is brightness reversion or fading ofpapers and fibers. The present invention advances the state of theseprior arts.

Although there are many ways to produce opaque media, this invention isconcerned with creating opacity by stretching or orienting plasticmaterials to induce microvoids which scatter light, preferable whitelight. A large body of prior art deals with this technique, wherein aplurality of inorganic solid particles are used as the dispersed phase,around which the microvoids form. Some significant problems associatedwith this approach are: (1) agglomeration and particle size control, (2)abrasive wear of extrusion equipment, guides, and cutters, (3) highspecific gravity of these solids, (4) poor void nucleation around thesolid particles due to the low thermal contraction of solids relative toliquids and polymer wetting and adhhesion to the solid surfaces, (5)cost of these materials on a volume basis, and (6) handling andprocessing problems in general. In every case, the invention reduces oreliminates the problem.

The prior art also teaches a variety of methods of creating surfacetexture. Often the surface is roughened by physical means like abrasion,crimping, etc. Many chemical methods are also used to react with, etch,or otherwise alter the surface. Flame, electrical corona, andelectromagnetic radiations are often employed. Coating technology iswell advanced for filling and whitening, and often inorganic materialsare major components of these coatings. Even if the orientation orstretching step is eliminated, a coating step is required. Not only domost of the problems above remain, but new ones are created in suchareas as adhesion, uniformity, and coating stability.

The cited prior art concentrates on synthetic paper compositions andmethods of manufacturing directly related to this invention, namelycompositions of matter involving polyesters and/or cellulose esters,stretching incompatible/immiscible thermoplastic blends to create voidedstructures with or without texture, and some of the properties andproblems associated with the use of inorganic, non-melting materials.The blend compositions and processing methods of this inventionconstitute a significant improvement over the immiscible polymer blendsystems found in the prior art.

DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view in section illustrating an embodiment ofthe present invention;

FIG. 2 is a perspective view in section illustrating another embodimentof the present invention;

FIG. 3 is a perspective view illustrating still another embodiment ofthe present invention;

FIG. 4 is a section of a shaped article in the form of a bottle;

FIG. 5 is an enlarged section view illustrating a microbead of celluloseacetate entrapped in a void in a polyester continuous matrix;

FIG. 6 is a sectional view taken along lines 6--6 of FIG. 5;

FIG. 7 is a sectional view similar to FIG. 5 illustrating a modificationof the present invention; and

FIG. 8 is a graphical representation illustrating how the size ofmicrobeads surrounding microbeads changes with respect to stretch ratio.

FIGS. 9, 10 and 11 are photomicrographs of film comprising a polyestercontinuous matrix, and cellulose ester microbeads at least partiallybordered by voids.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, shaped articles are providedwhich have unique properties such as texture and opacity. The articlesare especially useful when in the form of film or sheet material (e.g.,as a paper substitute) or when in the form of a biaxially orientedbottle (beverage container).

Referring to the drawings, FIG. 1 illustrates a shaped article in theform of a sheet 10 which has been biaxially oriented [biaxiallystretched, i.e., stretched in both the longitudinal (X) and transverse(Y) directions], as indicated by the arrows. The sheet 10 is illustratedin section, showing microbeads of cellulose acetate 12 contained withincircular voids 14 in the polyester continuous matrix 16. The voids 14surrounding the microbeads 12 are theoretically doughnut-shaped, but areoften of irregular shape. Sometimes two or more microbeads will bebordered by common voids, as illustrated in FIGS. 9, 10 and 11. Often, aline drawn perpendicular to and through the article will penetrateseveral voids and possibly some microbeads.

FIG. 2 also illustrates a shaped article in the form of a sheet 20 whichhas been unidirectionally oriented (stretched in one direction only, asindicated by the arrow). Microbeads of cellulose acetate 22 arecontained between microvoids 24 and 24'. The microvoids in this instanceform at opposite sides of the microbeads as the sheet is stretched.Thus, if the stretching is done in the machine direction (X) asindicated by the arrow, the voids will form on the leading and trailingsides of the microbeads. This is because of the unidirectionalorientation as opposed to the bidirectional orientation of the sheetshown in FIG. 1. This is the only difference between FIG. 1 and 2. Noteparticularly the bumpy texture of the surfaces.

FIG. 3 illustrates a shaped article in the form of a fiber or rod 30which has been oriented by stretching in the lengthwise (X) direction.The microbeads 32 of cellulose ester are bordered by microvoids 34 and34.

FIG. 4 illustrates a section of the wall of a shaped article 40 such asa bottle or wire coating. Due to the bidirectional orientation orstretching, the microvoids 42 are generally doughnut-shaped, surroundingthe microbeads 44, in a manner similar to that shown in FIG. 1.

FIGS. 5 and 6 are sectional views illustrating enlargement of a sectionof a shaped article according to this invention, microbead 50 beingentrapped within polyester continuous matrix 52 and encircled by void54. These structures result from the shaped article being stretched inthe X and Y directions.

FIG. 7 is a view similar to FIG. 5, except illustrating in enlarged formmicrobead 60 entrapped in polyester continuouos matrix 62, having formedon opposite sides thereof microvoids 64 and 64', which are formed as theshaped article is stretched in the direction of the arrow X.

FIG. 8 is an enlargement illustrating the manner in which microvoids areformed in the polyester continuous matrix as the shaped article isstretched or oriented. The formation of the microvoids 70 and 70' aroundmicrobeads 72 is illustrated on a stretch ratio scale as the shapedarticle is stretched up to 4 times its original dimension. For example,as the article is stretched 4 times its original dimension in the Xdirection (4×), the voids 70 and 70' would extent to the points 74 and74' respectively.

FIGS. 9 and 10 are actual photographs of sections of a sheet accordingto this invention which has been frozen and fractured. The continuousmatrix, microbeads and voids are obvious. FIG. 11 is an actualphotograph of a section of sheet material, oriented in one direction.The scale of these photomicrographs is indicated at the top of each inmicrons (um).

According to the present invention, there are provided shaped articlescomprising a continuous thermoplastic polyester phase having dispersedtherein microbeads of cellulose ester which are at least partiallybordered by voids. The shaped articles are conveniently in the form ofsheets or film, rods or fibers, bottles, wire coatings, etc. Thepolyester is relatively strong and tough, while the cellulose acetate isrelatively hard and brittle.

More specifically, the present invention provides shaped articlescomprising a continuous thermoplastic polyester phase having dispersedtherein microbeads of cellulose ester which are at least partiallybordered by voids, the microbeads of cellulose acetate being present inan amount of about 10-30% by weight based on the weight of polyester,the voids occupying about 2-50% by volume of the shaped article, thecomposition of the shaped article when consisting only of the polyestercontinuous phase and microbeads of cellulose ester bordered by voidscharacterized by having a Kubelka-Munk R value (infinite thickness) ofabout 0.90 to about 1.0 and the following Kubelka-Munk values whenformed into a 3 mil thick film:

Opacity -- about 0.78 to about 1.0

SX -- 25 or less

KX -- about 0.001 to 0.2

Ti -- about 0.02 to 1.0

wherein the opacity values indicate that the article is opaque, the SXvalues indicate a large amount of light scattering through the thicknessof the article, the KX values indicate a low amount of light absorptionthrough the thickness of the article, and the Ti values indicate a lowlevel amount of internal transmittance of the thickness of the article.The R (infinite thickness) values indicate a large amount of lightreflectance.

Obviously, the Kubelka-Munk values which are dependent on thickness ofthe article must be speciified at a certain thickness. Although theshaped articles themselves may be very thin, e.g., less than 1 mil orthey may be thicker, e.g., 20 mils, the Kubleka-Munk values, except forR infinity, are specified at 3 mils and in the absence of any additiveswhich would effect optical properties. Thus, to determine whether shapedarticles have the optical properties called for, the polyestercontaining microbeads at least partially bordered by voids, withoutadditives, should be formed in a 3 mils thick film for determination ofKubleka-Munk values.

The shaped articles according to this invention are useful, for example,when in the forms of sheets of films, bottles, ribbons, fibers or rods,wire coatings, etc. In the absence of additives or colorants, they arevery white, have a very pleasant feel or hand and very receptive to inkfrom writing instruments, especially conventional ball point pens. Infact, one of the most important uses contemplated for the presentinvention is as a synthetic paper for writing on or for prints such asdrawings. The shaped articles are very resistant to wear, moisture, oil,tearing, etc.

The polyester (or copolyester) phase may be any article-formingpolyester such as a polyester capable of being cast into a film orsheet, spun into fibers, extruded into rods or extrusion, blow-moldedinto containers such as bottles, etc. The polyesters should have a glasstransition temperature between about 50° C. and about 150° C.,preferably about 60°-100° C., should be orientable, and have an I.V. ofat least 0.55, preferably 0.6 to 0.9. Suitable polyesters include thoseproduced from aromatic, aliphatic or cycloaliphatic dicarboxylic acidsof 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24carbon atoms. Examples of suitable dicarboxylic acids includeterephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid,succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic,1,4-cyclohexanedicarboxylic, and mixtures thereof. Examples of suitableglycols include ethylene glycol, propylene glycol, butanediol,pentanediol, hexanediol, 1,4-cyclohexanedimethanol diethylene glycol andmixtures thereof. Such polyesters are well known in the art and may beproduced by well-known techniques, e.g., those described in U.S. Pat.Nos. 2,465, 319 and 2,901,466. The preferred polyester is polyethyleneterephthalate having a Tg of about 80° C. Other suitable polyestersinclude liquid crystal copolyesters formed by the inclusion of asuitable amount of a co-acid component such as stilbene dicarboxylicacid. Examples of such liquid crystal copolyesters are those disclosedin U.S. Pat. Nos. 4,420,607, 4,459,402 and 4,468,510.

Blends of polyesters and/or copolyesters are useful in the presentinvention. Also, small amounts of other polymers such as polyolefins canbe tolerated in the continuous matrix.

Suitable cellulose acetates are those having an acetyl content of about28 to 44.8% by weight, and a viscosity of about 0.01-90 seconds. Suchcellulose acetates are well known in the art. Small contents ofpropionyl can usually be tolerated. Also, processes for preparing suchcelliulose acetates are well known in the art. Suitable commerciallyavailable cellulose acetates include the following which are marketed byEastman Chemical Products, Inc.:

    __________________________________________________________________________    Cellulose      Acetyl                                                                             Hydroxyl                                                                           Melting   Number Average                             Acetate                                                                             Viscosity.sup.1                                                                        Content                                                                            Content                                                                            Range                                                                              Tg,  Molecular                                  Type  Seconds                                                                            Poises                                                                            %.sup.2                                                                            %.sup.2                                                                            °C.                                                                         °C.                                                                         Weight.sup.3                               __________________________________________________________________________    CA-394-60S                                                                          60.0 228.0                                                                             39.5 4.0  240-260                                                                            186  60,000                                     CA-398-3                                                                            3.0  11.4                                                                              39.8 3.5  230-250                                                                            180  30,000                                     CA-398-6                                                                            6.0  22.8                                                                              39.8 3.5  230-250                                                                            182  35,000                                     CA-398-10                                                                           10.0 38.0                                                                              39.8 3.5  230-250                                                                            185  40,000                                     CA-398-30                                                                           30.0 114.0                                                                             39.7 3.5  230-250                                                                            189  50,000                                     CA-320S                                                                             0.05 0.2 32.0 8.4  190-269                                                                            about                                                                              about                                                                    180-190                                                                            18,000                                     CA-436-80S                                                                          80   304 43.7  0.82                                                                              269-300                                                                            180  102,000                                    __________________________________________________________________________     .sup.1 ASTM D817 (Formula A) and D1343                                        .sup.2 ASTM D817                                                              .sup.3 Molecular weights are polystyrene equivalent molecular weights,        using Gel Permeation Chromatography                                      

The microbeads of cellulose esters range in size from about 0.1-50microns, and are present in an amount of about 10-30% by weight based onthe weight of the polyester. The microbeads of cellulose acetate havinga Tg of at least 20° C. higher than the Tg of the polyester and are hardcompared to the polyester.

The microbeads of cellulose acetate are at least partially bordered byvoids. The void space in the shaped article should occupy about 2-50%,preferably about 20-30%, by volume of the shaped article. Depending onthe manner in which the shaped articles are made, the voids maycompletely encircle the microbeads, e.g., a void may be in the shape ofa doughnut (or flattened doughnut) encircling a microbead, or the voidsmay only partially border the microbeads, e.g., a pair of voids mayborder a microbead on opposite sides.

The invention does not requuire but permits the use or addition of aplurality of organic and inorganic materials such as fillers, pigments,antiblocks, anti-stats, plasticizers, dyes, stabilizers, nucleatingagents, etc. These materials may be incorporated into the matrix phases,into the dispersed phases, or may exist as separate dispersed phases.

The microvoids form on cooling without requiring nucleating agents.During stretching the voids assume characteristic shapes from thebalanced biaxial orientation of paperlike films to the uniaxialorientation of microvoided/satin-like fibers. Balanced microvoids arelargely circular in the plane of orientation while fiber microvoids areelongated in the direction of the fiber axis. The size of the microvoidsand the ultimate physical properties depend upon the degree and balanceof the orientation, temperature and rate of stretching, crystallizationkinetics, the size distribution of the microbeads, and the like.

The shaped articles according to this invention are prepared by

(a) forming a mixture of molten polyester and cellulose acetate whereinthe cellulose acetat is a multiplicity of microbeads uniformly dispersedthroughout the polyester, the polyester being as described hereinbefore,the cellulose acetate being as described hereinbefore.

(b) forming a shaped article from the mixture by extrusion, casting ormolding,

(c) orienting the article by stretching to form microbeads of celluloseacetate uniformly distributed throughout the article and voids at leastpartially bordering the microbeads on sides thereof in the direction, ordirections of orientation.

The mixture may be formed by forming a melt of the polyester and mixingtherein the cellulose acetate. The cellulose acetate may be in the formof solid or semi-solid microbeads, or in molten form. Due to theincompatability between the polyester and cellulose acetate, there is noattraction or adhesives between them, allowing the cellulose acetate to"bead-up" if molten to form dispersed microbeads upon mixing. If solidor semi-solid, the microbeads become uniformly dispersed in thepolyester upon mixing.

When the microbeads have become uniformly dispersed in the polyester, ashaped article is formed by processes such as extrusion, casting ormolding. Examples of extrusion or casting would be extruding or castinga film or sheet, and an example of molding would be injection or reheatblow-molding a bottle. Such forming methods are well known in the art.If sheets or film material are cast or extruded, it is important thatsuch article be oriented by stretching, at least in one direction.Methods of unilaterally or bilaterally orienting sheet or film materialare well known in the art. Basically, such methods comprise stretchingthe sheet or film at least in the machine or longitudinal directionafter it is case or extruded an amount of about 1.5-10 (usually 3-4)times its original dimension. Such sheet or film may also be stretchedin the transverse or cross-machine direction by apparatus and methodswell known in the art, in amounts of generally 1.5-10 (usually 3-4)times the original dimension. Such appratus and methods are well knownin the art and are described in such U.S. Pat. Nos. 3,903,234,incorporated herein by reference.

If the shaped article is in the form of a bottle, orientation isgenerally biaxial as the bottle is stretched in all directions as it isblow-molded. Such formation of bottles is also well known in the art.See, for example, U.S. Pat. No. 3,849,530, incorporated herein byreference.

The voids, or void spaces, referred to herein surrounding the microbeadsare formed as the polyester continuous matrix is stretched at atemperature between the polyester Tg and the cellulose acetate Tg. Themicrobeads of cellulose acetate are relatively hard compared to thepolyester continuous matrix. Also, due to the incompatability andimmiscibility between the cellulose acetate and the polyester, thepolyester continuous matrix slides over the microbeads as it isstretched, causing voids to be formed at the sides in the direction ordirections of stretch, which voids elongate as the polyester matrixcontinues to be stretched. Thus, the final size and shape of the voidsdepends on the direction(s) and amount of stretching. If stretching isonly in one direction, microvoids will form at the sides of themicrobeads in the direction of stretching. If stretching is in twodirections (bidirectional stretching), in effect such stretching hasvector components extending radially from any given position to resultin a doughnut-shaped void surrounding each microbead.

The preferred preform stretching operation simultaneously opens andmicrovoids and orients the matrix material. The final product propertiesdepend on and can be controlled by stretching time-temperaturerelationships and on the type and degree of stretch. For maximum opacityand texture, the stretching is done just above the glass transitiontemperature of the matrix material. When stretching is done in theneighborhood of the higher glass transition temperature, both phasesstretch together and opacity decreases. In the former case, thematerials are pulled apart, a mechanical anticompatibilization process,In the latter case, they are drawn together, a mechanicalcompatibilization process. Two examples are high-speed melt spinning offibers and melt blowing of fibers and films to formnon-woven/spun-bonded products. In summary, the scope of this inventionincludes the complete range of forming operations just described.

In general, void formation occurs independent of, and does not require,crystalline orientation of the matrix phase. Opaque, microvoided filmshave been made in accordance with the methods of this invention usingcompletely amorphous, non-crystallizing copolyesters as the matrixphase. Crystallizable/orientable (strain hardening) matrix materials arepreferred for some properties like tensile strength and barrier. On theother hand, amorphous matrix materials have special utility in otherareas like tear resistance and heat sealability. The specific matrixcomposition can be tailored to meet many product needs. The completerange from crystalline to amorphous matrix materials is part of theinvention.

Stretching experiments reveal that increasing the cellulose estercontent of the blends reduces the effective natural draw ratio relativeto that of the matrix material and raises the effective orientation ordraw temperature. When melt casting these films, required casting rolltemperature increases with cellulose ester content. Minimal coolingbelow the orientation temperature prior ro stretching is preferred sincethe cooled preform state is often brittle, the brittleness increasingwith cellulose ester content. This is not a problem in blowing bottlesfrom reheated injection-molded preforms.

Another important and useful property of these microvoided structures isthe irreversible closure of the microvoids under the action of directpressure. Although cell/void closure phenomena are not new, the films ofthis invention represent an improvement over the prior art. Highresolution, clear light paths are created in these partially opaque,light-diffusing films when the microvoids close around the clear,cellulose ester microbeads. These closures can be accomplished before orafter heat-setting and also survive the heat-setting process. The filmsof this invention are useful for recording information suitable forreading by light sensing devices or projecting by transmitted light.Instant slides have been made by inkless writing and typing on thesefilms, mounting in a slide frame, and heat shrinking. When projectedonto a screen with a conventional slide projector, precise, bright,white images on a soft gray background are seen. When colors areincorporated into the films, precise, bright, tinted-white images onsoft tinted-gray background are seen. When these films are pressureprinted with transparent colors, precise, bright, colored images arecreated. Use of the compositions and products of this invention formicrovoided recording and projection media are the result of and part ofthe invention.

The following examples are submitted for a better understanding of theinvention.

In the examples the specified materials were combined and mixed in a drystate prior to extrusion. Most of the materials used in these examplesare granules (ground through a 2 millimeter screen) and fine powders.This form permits good dry blending without separation duringprocessing. In most cases, the mixed materials were dried under vacuumconditions with nitrogen bleed to carry off the volatiles. Of course,when substantial amounts of low-melting materials were used, separatedrying was done, followed by mixing and immediate extrusion. Therelative amounts of the polyester, cellulose ester, and other materialsare indicated by mass ratios; and all percents are weight %. Duringextrusion, the materials are melted and mixed as viscous melts. Shearemulsification of the immiscible melts was enhanced with a mixingsection centrally located in the metering section of the extruder screw.Residence time was kept small by design; for example, screw L/D was 24:1(Killion 1.25 inch extruder) and the dies were joined directly to theextruder via small-sized adaptors. The extrudate is quenched to formflat films or sheet, tubular films, rods, fibers, or bottle preforms(injection molding). The required orientaton was carried out byconventional equipment and methods associated with the specific formingoperation.

EXAMPLE 1

Blends were prepared with a polyester and a cellulose acetate. Thepolyester is Polyester A and the cellulose ester is cellulose acetateCA-398-30. Two blends (80/20) and (90/10) were melt cast to form sheetsbetween 15 to 20 mils thick. These sheets were simultaneously stretched4× (a multiple of 4) in both directions to form white, paper-like filmsjust over 1 mil thick. The films of this invention are highly diffusereflective over the visible spectrum and remain highly reflective in thenear UV (300 to 400 nanometer wavelengths) region. Typical filmsproperties and processing conditions are given below.

EXAMPLE 2 (Control)

This example is an example of prior art. It is given here for directcomparison with Example 1. Blends were prepared with the same polyesteras Example 1 and inorganic materials. The inorganics are titaniumdioxide (Rutile R-100) and calcium carbonate (Microwhite 25). A (90/10)blend of the polyester and each of the inorganics was melt cast to formsheets between 15 to 20 mils thick. These sheets were simultaneouslystretched 4× in both directions to form white, plastic-like films justover 1 mil thick. Typical film properties and processing comditions aregiven below.

EXAMPLE 3

Blends were prepared with a polyester and a cellulose acetate. Thepolyester is a blend of polyester A and Polyester A containing acovalently bound colorant. The cellulose acetate is CA-398-30. Two(80/20) blends (one containing 0.5% red moiety and one containing 0.5%blue moiety) were melt cast to form sheets about 20 mils thick. Thesesheets were simultaneously stretched 4× in both directions to formpastel-colored, paper-like films about 1.75 mils thick. Typical filmproperties and processing conditions are given below.

EXAMPLE 4

Blends were prepared with a polyester and a mixed cellulose ester,cellulose acetate propionate. The polyester is Polyester A and thecellulose ester is CAP-482-20. This (90/10) blend and a (90/10) blendmade like Example 1 were melt cast to form sheets about 15 mils thick.These sheets were simultaneously stretched 4× in both directions to formtranslucent, paper-like films about 1 mil thick. Typical film propertiesand processing conditions are given below.

EXAMPLE 5

Blends were prepared with the same polyester and cellulose acetate asExample 1. The specific blends (95/5), (90/10), (85/15), (80/20),(75/25), and (70/30) were melt cast to form sheets about 25 mils thick.Extrusion conditions were similar to those of Example 1. These sheetswere simultaneously stretched 3× in both directions to form white,paper-like films about 3 mils thick. These sheets were alsosimultaneously stretched 4× in both directions to form white, paper-likefilms about 2 mils thick. Typical film optical properties are givenbelow.

EXAMPLE 6

This example shows that light-colored, opaque structures developed whenthe dispersed phase was colored. The polyester of Example 1 was mixedwith a cellulose acetate (CA-320S, containing a covalently bondedcolorant). A (90/10) blend (containing 0.13% red moiety) was melt castto form sheets about 15 mils thick. These sheets were stretched as inExample 1 yielding uniformly pastel-red, opaque, paper-like films.

EXAMPLE 7

This example shows that lower viscosity polyesters containing minoramounts of additives yielded products of this invention. A blend wasprepared with a polyester and a cellulose acetate. The polyester isPolyester B and the cellulose acetate is CA-398-30. A (90/10) blend wasmelt cast to form sheets between 15 to 20 mils thick. A Brabender 3/4inch laboratory extruder without a mixing screw was used at 110 RPM and260° C. (melt temperature). These sheets were simultaneously stretched4× in both directions to form white, paper-like films just over 1 milthick. The effect of the optical brightener was visually observed to beenhanced by the highly reflective structures of this invention. Thesefilms contained visible particles of cellulose acetate resulting fromthe incomplete shear emulsification on this machine.

EXAMPLE 8

This example shows that white, opaque properties developed over a rangeof stretching conditions. A (90/10) blend of the same materials asExample 1 was melt cast using the equipment of Example 6. Stretchingconditions were (2×1), (2×2), (3×1), (3×2), (3×3), (4×1), (4×2), (4×3)and (4×4). Whiteness and opacity were visually evident at all levels ofstretching, increasing with balance and degree of stretch.

EXAMPLE 9

This example illustrates that polyester/polyester blends can be usedwith cellulose acetates to produce articles of this invention. Thespecific blends of this example are (65/25/10) and (65/15/20) usingPolyester A, Polyester C, and CA-398-30 respectively. Films were made asin Example 1, and the resulting properties were similar. The films ofthis example, however, were more flexible due to the presence of thethermoplastic elastomer in the blend.

EXAMPLE 10

Blends were prepared with a polyester and a cellulose acetate. Thepolyester is Polyester A and the cellulose acetate is CA-394-60S. Thefollowing blends (95/5), (90/10), (85/15), and (80/20) were meltextruded and simultaneously biaxially oriented on a laboratory blownfilm line. The oriented tubes had a layflat width of about 9 to 12inches, and the film thickness was about 0.5 mil. These films werewhite, opaque, and had tissue paper qualities. Typical film propertiesand processing conditions are given below.

EXAMPLE 11

Blends were prepared with a polyester and a cellulose acetate. Thepolyester is a blend of Polyester A and Polyester A containing acovalently bound colorant. The cellulose acetate is CA-398-30. Four(80/20) blends were melt extruded and simultaneously biaxially orientedas in Example 10. Typical film properties and processing conditions aregiven below.

EXAMPLE 12

A (90/10) blend were prepared with a higher glass transition polyester,Polyester D, and a cellulose acetate (CA-394-60S). This blend was meltextruded at a melt temperature of 270° C. and simultaneously biaxiallyoriented at about 140° C. as in Example 10. The resulting film waswhite, opaque, and paper-like. The quality was slightly degraded becausethe polyester was recycled material. This blend system is especiallyattractive if high temperature resistant products are beingmanufactured.

EXAMPLE 13

The blends of this example were prepared from a polyester, apolypropylene, and a cellulose acetate. The polyester is Polyester A;the polypropylene homopolymer is PP 4230; and the cellulose acetate isCA-394-60S. Three blends (70/10/20), (75/5/20), and (77/3/20) were meltextruded and simultaneously biaxially oriented as in Example 10. White,opaque, paper-like films were made, however film strength and qualitydecreased as the level of polypropylene increased.

EXAMPLE 14

A (90/10) blend was prepared with a polyester, Polyester A, and acellulose triacetate CA-436-80S. This blend was melt extruded at a melttemperature of 275° C. and simultaneously biaxially oriented as inExample 10. White, opaque, paper-like films were made, however thequality of the film was degraded by the presence of small particles ofincompletely melted cellulose triacetate.

EXAMPLE 15

Blends were prepared with a polyester, Polyester A, a water-dispersiblepolyester, and a cellulose acetate (CA-398-30). The blend was meltextruded and simultaneously biaxially oriented as in Example 10. Thewhite, opaque, paper-like films were of good quality, with an enhancedhydrophilic character due to the presence of the hydrophilic polyester.

EXAMPLE 16

A (90/10) blend of an amorphous copolyester and a cellulose acetate wasprepared. The copolyester was Polyester E, and the cellulose acetate wasCA-394-60S. The blend was melt extruded and simultaneously biaxiallyoriented as in Example 10; however, the white, opaque, paper-like filmshad a faint, yellowish tint, indicating greater thermal degradation.

EXAMPLE 17

A (90/10) blend of another copolyester and a cellulose acetate wasprepared. The copolyester was Polyester F and the cellulose acetate wasCA-398-30. The blend was melt extruded and simultaneously biaxiallyoriented as in Example 10. A good quality, white, opaque, paper-likefilm resulted.

EXAMPLE 18

A (90/10) blend was prepared from a polyester, Polyester A, and a lowerviscosity cellulose acetate (CA-398-3). A second (90/10) blend of thispolyester with a lower % acetyl cellulose acetate (CA-320S) was alsoprepared. Both blends were melt extruded and simultaneously biaxiallyoriented as in Example 10. Good quality, white, opaque, paper-like filmsresulted. In addition, both blends were melt extruded as in Example 10,followed by uniaxial (machine direction) drawing in the second bubble.This procedure was used to create tubular or hollow fiber analogs.Relatively strong, white, opaque, textured-surface structures containinguniaxially drawn microvoids were observed. Fiber structures were alsoproduced by reheating and hand-drawing strands cut from cast sheets.

EXAMPLE 19

Another (90/10) blend of polyester, Polyester A, and cellulose acetate(CA-398-30) was melt extruded on a New Britain injection-molding machineto made standard 55 gram preforms (parisons) for 2-liter orientedpolyester beverage bottles. The preforms were reheated and blown at amanual blowing station to produce white, opaque, textured, orientedbotles. The surface of these bottles was noticeably rough when comparedwith the films and fibers. This was a result of the poor mixingconditions in the injection-molding machine, a cyclic opertion without amixing screw.

    ______________________________________                                        EXAMPLE 1                                                                     TYPICAL CAST & TENTERED FILM PROPERTIES                                       FOR 80/20 & 90/10 POLYESTER/CELLULOSE ACETATE                                 Material     (80)   Polyester A                                                                              (90) Polyester A                                            (20)   CA-398-30  (10) CA-398-30                                 Melt Temp., °C.                                                                     260           262                                                Screw Speed (rpm)                                                                          50            50                                                 Cast Roll Temp., °C.                                                                82            58                                                 Cast Roll Speed (fpm)                                                                      6.0           --                                                 Stretch Temp., °C.                                                                  120           110                                                Film Thickness (mil)                                                                       1.37          1.17                                               Inherent Visc. (dl/g)                                                                      0.590         0.623                                              Density (g/cc)                                                                             1.023         1.303                                              Tensile Yield (10.sup.3 psi)                                                               7.40/6.67     12.8/12.6                                          Tensile Break (10.sup.3 psi)                                                               10.4/8.74     23.5/22.4                                          Elongation to Break                                                                        70/61         92/77                                              (%)                                                                           Oxygen Transmission                                                                        16.0          9.54                                               (cc-mil/100 in.sup.2 hr-atm)                                                  Kubelka-Munk                                                                  Analysis (560 nm):                                                            Scattering SX                                                                              3.644         2.308                                              Absorption KX                                                                              0.002x        0.002x                                             Transmittance T(i)                                                                         0.214         0.302                                              Reflectance R(inf)                                                                         0.966         0.966                                              Opacity      0.812         0.722                                              ______________________________________                                    

    ______________________________________                                        EXAMPLE 2                                                                     CAST & TENTERED FILM PROPERTIES                                               FOR 90/10 POLYESTER/INORGANIC FILLER                                          Material      (90) Polyester A                                                                           (90) Polyester A                                                 (10) Rutile R-100                                                                          (10) Microwhite 25                                 Melt Temp., °C.                                                                      263          263                                                Screw Speed (rpm)                                                                           50           50                                                 Cast Roll Temp., °C.                                                                 42           50                                                 Cast Roll Speed (fpm)                                                                       --           --                                                 Stretch Temp., °C.                                                                   110          110                                                Film Thickness (mil)                                                                        1.13         1.33                                               Inherent Visc. (dl/g)                                                                       0.563        0.573                                              Density (g/cc)                                                                              1.432        1.323                                              Tensile Yield (10.sup.3 psi)                                                                11.3/12.0    10.8/11.2                                          Tensile Break (10.sup.3 psi)                                                                18.6/20.3    16.5/17.7                                          Elongation to Break (%)                                                                     103/100      73/71                                              Oxygen Transmission                                                                         8.72         10.2                                               (cc-mil/100 in.sup.2 hr-atm)                                                  Kubelka-Munk Analysis                                                         (560 nm):                                                                     Scattering SX 2.310        1.115                                              Absorption KX 0.005x       0.008x                                             Transmittance T(i)                                                                          0.300        0.468                                              Reflectance R(inf)                                                                          0.936        0.886                                              Opacity       0.742        0.591                                              ______________________________________                                    

    __________________________________________________________________________    EXAMPLE 3                                                                     FOR 75/5/20 POLYESTER/RED POLYESTER/CELLULOSE ACETATE                         75/5/20 POLYESTER/BLUE POLYESTER/CELLULOSE ACETATE                            Material    (75)                                                                             Polyester A                                                                            (75)                                                                             Polyester A                                                    (5)                                                                              Polyester A (Red)                                                                      (5)                                                                              Polyester A (Blue)                                             (20)                                                                             CA-398-30                                                                              (20)                                                                             CA-398-30                                          Melt Temp., °C.                                                                    260         260                                                   Screw Speed (rpm)                                                                         50          50                                                    Cast Roll Temp., °C.                                                               82          82                                                    Cast Roll Speed (fpm)                                                                     6.0         6.0                                                   Stretch Temp., °C.                                                                 120         125                                                   Film Thickness (mil)                                                                      1.78        1.75                                                  Inherent Visc. (dl/g)                                                                     0.640       0.672                                                 Density (g/cc)                                                                            0.889       0.895                                                 Tensile Yield (10.sup.3 psi)                                                              6.19/6.00   4.97/4.92                                             Tensile Break (10.sup.3 psi)                                                              8.10/7.75   5.78/5.38                                             Elongation to Break (%)                                                                   50/42       41/23                                                 Oxygen Transmission                                                                       18.4        21.8                                                  (cc-mil/100 in.sup.2 hr-atm)                                                  Kubelka-Munk Analysis                                                         (560 nm):                                                                     Scattering SX                                                                             5.571       6.530                                                 Absorption KX                                                                             2.332x      2.408x                                                Transmittance T(i)                                                                        0.003       0.000                                                 Reflectance R(inf)                                                                        0.413       0.434                                                 Opacity     1.000       1.000                                                 __________________________________________________________________________

    ______________________________________                                        EXAMPLE 4                                                                     CAST & TENTERED FILM PROPERTIES                                               FOR 90/10 POLYESTER/CELLULOSE ACETATE AND                                     90/10 POLYESTER/CELLULOSE ACETATE PROPIONATE                                  Material       (90) Polyester A                                                                           (90) Polyester A                                                 (10) CA-398-30                                                                             (10) CAP-482-20                                   Melt Temp., °C.                                                                       264          264                                               Screw Speed (rpm)                                                                            50           50                                                Cast Roll Temp., °C.                                                                  49           49                                                Cast Roll Speed (fpm)                                                                        6.0          6.0                                               Stretch Temp., °C.                                                                    105          115                                               Film Thickness (mil)                                                                         1.03         0.94                                              Inherent Visc. (dl/g)                                                                        0.603        0.665                                             Density (g/cc) 1.192        1.364                                             Tensile Yield (10.sup.3 psi)                                                                 13.5/13.7    15.9/15.1                                         Tensile Break (10.sup.3 psi)                                                                 25.5/25.9    29.0/29.2                                         Elongation to Break (%)                                                                      84/78        103/108                                           Oxygen Transmission                                                                          8.01         7.34                                              (cc-mil/100 in.sup.2 hr-atm)                                                  Kubelka-Munk Analysis                                                         (560 nm):                                                                     Scattering SX  2.397        0.398                                             Absorption KX  0.006x       0.006x                                            Transmittance T(i)                                                                           0.292        0.711                                             Reflectance R(inf)                                                                           0.930        0.848                                             Opacity        0.756        0.334                                             ______________________________________                                    

    __________________________________________________________________________    EXAMPLE 5                                                                     KUBELKA-MUNK ANALYSES                                                         Polyester/                                                                             Stretch                                                                            Stretch                                                                           Reheat                                                      Cellulose Acetate                                                                      Ratios                                                                             Temp.,                                                                            Time                                                                              Thickness                                                                           Kubelka-Munk Values                               (Mass Ratio)                                                                           (X × Y)                                                                      °C.                                                                        (Sec)                                                                             (Mils)                                                                              SX  KX  T(i)                                                                             Roo                                                                              Opacity                             __________________________________________________________________________    99/1     3 × 3                                                                        100 45  2.7   0.201                                                                             0.012X                                                                            0.822                                                                            0.710                                                                            0.233                               98/2     3 × 3                                                                        100 45  2.8   0.272                                                                             0.014X                                                                            0.775                                                                            0.730                                                                            0.289                               95/5     3 × 3                                                                        100 60  2.9   0.861                                                                             0.013X                                                                            0.529                                                                            0.838                                                                            0.545                               90/10    3 × 3                                                                        100 75  3.2   2.611                                                                             0.014X                                                                            0.271                                                                            0.901                                                                            0.794                               85/15    3 × 3                                                                        100 75  3.7   6.484                                                                             0.015X                                                                            0.128                                                                            0.933                                                                            0.917                               80/20    3 × 3                                                                        100 75  4.0   11.892                                                                            0.013X                                                                            0.073                                                                            0.954                                                                            0.958                               75/25    3 × 3                                                                        100 60  3.4   12.126                                                                            0.016X                                                                            0.071                                                                            0.950                                                                            0.961                               70/30    3 × 3                                                                        110 75  5.2   19.160                                                                            0.015X                                                                            0.045                                                                            0.961                                                                            0.978                               75/25    3.5 × 3.5                                                                    115 60  2.7   7.262                                                                             0.012X                                                                            0.117                                                                            0.945                                                                            0.922                               70/30    3.5 × 3.5                                                                    115 60  5.0   21.990                                                                            0.012X                                                                            0.040                                                                            0.967                                                                            0.980                               99/1     4 × 4                                                                        110 60  1.6   0.195                                                                             0.011X                                                                            0.828                                                                            0.719                                                                            0.224                               98/2     4 × 4                                                                        110 60  1.6   0.260                                                                             0.011X                                                                            0.785                                                                            0.749                                                                            0.273                               95/5     4 × 4                                                                        110 60  1.8   0.745                                                                             0.010X                                                                            0.567                                                                            0.851                                                                            0.497                               90/10    4 × 4                                                                        110 60  2.1   2.583                                                                             0.010X                                                                            0.274                                                                            0.914                                                                            0.782                               85/15    4 × 4                                                                        115 60  2.0   4.076                                                                             0.009X                                                                            0.193                                                                            0.937                                                                            0.851                               80/20    4 × 4                                                                        115 45  2.7   9.699                                                                             0.011X                                                                            0.090                                                                            0.954                                                                            0.943                               70/30    4 × 4                                                                        120 120 5.8   22.634                                                                            0.015X                                                                            0.037                                                                            0.964                                                                            0.983                               __________________________________________________________________________

    __________________________________________________________________________    EXAMPLE 10                                                                    BLOWN FILM PROPERTIES                                                         Material or Blend                                                                          (95)                                                                             Polyester A                                                                          (90)                                                                             Polyester A                                                                          (85)                                                                             Polyester A                                                                          (80)                                                                             Polyester A                                  (5)                                                                              CA-394-60S                                                                           (10)                                                                             CA-394-60S                                                                           (15)                                                                             CA-394-60S                                                                           (20)                                                                             CA-394-60S                      Extruder Melt Temp., °C.                                                            255       254       260       260                                Extruder Pressure                                                                          1400      1400      1500      1400                               (psig)                                                                        Extruder Screw (rpm)                                                                       40        40        50        50                                 NIP Speed (ft/min)                                                                         46        46        43        51                                 Film Thickness                                                                             0.49      0.49      0.59      0.48                               (mil)                                                                         Area Weight (grams/                                                                        1.71      1.60      2.01      1.27                               sq ft)                                                                        Density (sp.gr.)                                                                           1.301     1.302     1.208     1.120                              Yield Stress (10.sup.3 psi)                                                                8.6/7.6   7.8/5.9   5.3/7.4   5.1/6.4                            (MD/TD)                                                                       __________________________________________________________________________

    __________________________________________________________________________    EXAMPLE 11                                                                    BLOWN FILM PROPERTIES                                                         Material or Blend                                                                           (80)                                                                             Polyester A                                                                          (75)                                                                             Polyester A                                                                              (75)                                                                             Polyester A                                                                            (80)                                                                             Polyester A                            (20)                                                                             CA-398-30                                                                            (5)                                                                              Polyester A (Yellow)                                                                     (5)                                                                              Polyester A (Red)                                                                      (5)                                                                              Polyester A (Blue)                               (20)                                                                             CA-398-30  (20)                                                                             CA-398-30                                                                              (20)                                                                             CA-398-30                Extruder Melt Temp., °C.                                                             255       255           256         257                         Extruder Pressure                                                                           1400      1400          1400        1400                        (psig)                                                                        Extruder Screw (rpm)                                                                        50        50            50          50                          NIP Speed (ft/min)                                                                          51        51            51          51                          Film Thickness                                                                              0.60      0.53          0.49        0.48                        (mil)                                                                         Area Weight (grams/                                                                         1.84      1.57          1.53        1.44                        sq ft)                                                                        Inherent Viscosity                                                                          0.629     0.650         0.660       0.657                       (dl/gm)                                                                       Density (sp.gr.)                                                                            1.143     1.143         1.109       1.117                       Yield Stress (10.sup.3 psi)                                                                 8.8/7.2   9.1/8.2       8.1/7.6     8.0/7.6                     (MD/TD)                                                                       Oxygen Transmission                                                                         11.5      12.2          11.7        11.8                        (cc-mil/100 in.sup.2 -                                                        24 hr-atm)                                                                    __________________________________________________________________________

    ______________________________________                                        Polyester A is described                                                      as follows:                                                                   Reaction Product Of:                                                          Dicarboxylic acid(s)                                                                            dimethyl terephthalate                                      or Ester Thereof                                                              Glycol(s)         ethylene glycol                                             I.V.              0.70                                                        Tg                about 80° C.                                         Tm                about 255° C.                                        Polyester B is described                                                      as follows:                                                                   Reaction Product Of:                                                          Dicarboxylic acid(s)                                                                            dimethyl terephthalate                                      or Ester Thereof                                                              Glycol(s)         ethylene glycol                                             I.V.              0.64                                                        Tg                about 80° C.                                         Tm                about 255° C.                                        Polyester C is described                                                      as follows:                                                                   Reaction Product Of:                                                          Dicarboxylic acid(s)                                                                            99.5 mol % 1,4-cyclo-                                                         hexanedicarboxylic                                                            acid                                                        or Ester Thereof  0.5 mol % trimellatic                                                         anhydride                                                   Glycol(s)         91.1 mol % 1,4-cyclo-                                                         hexanedimethanol                                                              8.9 mol % poly(tetra-                                                         methylene ether glycol)                                     I.V.              1.05                                                        Tg                below 0° C.                                          Tm                about 120° C.                                        Polyester D is described                                                      as follows:                                                                   Reaction Product Of:                                                          Dicarboxylic acid(s)                                                                            Naphthalene dicarboxylic                                    or Ester Thereof  acid                                                        Glycol(s)         ethylene glycol                                             I.V.              0.80                                                        Tg                125° C.                                              Tm                265° C.                                              Polyester E is described                                                      as follows:                                                                   Reaction Product Of:                                                          Dicarboxylic acid(s)                                                                            terephthalic acid                                           or Ester Thereof                                                              Glycol(s)         69 mol % ethylene glycol                                                      31 mol % 1,4-cyclo-                                                           hexanedimethanol                                            I.V.              0.75                                                        Tg                about 80° C.                                         Tm                amorphous                                                   Polyester F is described                                                      as follows:                                                                   Reaction Product Of:                                                          Dicarboxylic acid(s)                                                                            75 mol % terephthalic                                       or Ester Thereof  acid                                                                          25 mol % trans-4,4'-                                                          stilbene dicarboxylic                                                         acid                                                        Glycol(s)         ethylene glycol                                             I.V.              about 0.8                                                   Tg                95° C.                                               Tm                -215° C.                                             ______________________________________                                    

The cellulose acetates, designated as "CA" are as defined in the tableabove.

Where ratios or parts are given, e.g., 80/20, they are parts by weight,with the polyester weight specified first.

The following applies to Kubelka-Munk values:

SX is the scattering coefficient of the whole thickness of the articleand is determined as follows: ##EQU1## wherein: b=(a² -1)^(1/2)

Ar ctgh is the inverse hyperbolic cotangent ##EQU2## Ro is reflectancewith black tile behind sheet R is reflectance with white tile behindsheet

Rg is reflectance of a white tile=0.89

KX is the absorption coefficient of the whole thickness of the articleand is determined as follows:

    KX=SX(a-1)

wherein SX and a are as defined above

R (infinity) is the reflectance of an article if the article was sothick that additional thickness would not change it and is determined asfollows:

    R(infinity)=a-(a.sup.2 -1).sup.1/2

wherein a is as defined above

Ti is the internal light transmittance and is determined as follows:

    Ti=[(a-Ro).sup.2 -b.sup.2 ].sup.1/2 ##EQU3##  wherein Ro and Rg are as defined above.

In the above formulae, Ro, R and Rg are determined in a conventionalmanner using a Diano Match-Scan II Spectrophotometer (Milton Roy Co.)using a wavelength of 560 nanometers. Also above, X in the formulae SXand KX is the thickness of the article. A full description of theseterms is found in Colors in "Business, Science and Industry" 3rdEdition, by Deane B. Judd & Gunter Wyszecki, published by John Wiley &Sons, N.Y. (1975), pages 397-439, which is incorporated herein byreference.

Glass transition temperatures, Tg and melt temperatures, Tm, aredetermined using a Perkin-Elmer DSC-2 Differential Scanning Calorimeter.

In the examples, physical properties are measured as follows:

Tensile Strength at Yield -- ASTM D882

Tensile Strength at Break -- ASTM D882

Elongation at Break -- ASTM D882

Unless otherwise specified inherent viscosity is measured in a 60/40parts by weight solution of phenol-tetrachloroethane 25° C. and at aconcentration of about 0.5 gram of polymer in 100 ml of the solvent.

Where acids are specified herein in the formation of the polyesters orcopolyesters, it should be understood that ester forming derivatives ofthe acids may be used rather than the acids themselves as isconventional practice. For example, dimethyl isophthalate may be usedrather than iosphthalic acid.

In the exmaples, oxygen permeability is determined according to ASTM D3985, in cubic centimeters permeating a 1 mil thick sample, 100 inchessquare, for a 24-hour period under oxygen partial pressure difference ofone atmosphere at 30° C. using a MOCON Oxtran 10-50 instrument. Oxygenpermeability is also given in S.I. (Systems International) units incubic centimeters permeating a 1 cm. thick sample, 1 cm. square, for 1second at atmospheric pressure.

Unless otherwise specified, all parts, ratios, percentages, etc. are byweight.

The invention has been described in detail with particular reference topreferred embodiments theeof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. The method of forming a shaped article having at least onemajor surface comprising a continuous phase of polyester havingdispersed therein microbeads of cellulose acetate at least partiallybordered by void space oriented generally flatwise with respect to saidmajor surface of said shaped article, said sheet when consisting only ofsaid polyester continuous phase and said microbeads at least partiallybordered by void space characterized by having a Kubelka-Munk R value(infinite thickness) of about 0.90 to about 1.0 and the followingKubelka-Munk values when formed into a 3 mil thick film:Opacity -- about0.78 to about 1.0 SX -- 25 or less KX -- about 0.001 to 0.2 T(i) --about 0.02 to 1.0said method comprising (a) forming a mixture of moltenpolyester and cellulose acetate, wherein the cellulose acetate is amultiplicity of uniformly dispersed microbeads throughout saidpolyester, said polyester having an I.V. of at least 0.55, saidcellulose acetate having an acetyl content of about 28 to 44.8% byweight, a viscosity of about 0.01-90 seconds and a Tg of about 20° C.higher than the Tg of said polyester, (b) forming a shaped article fromsaid mixture, (c) orienting said article by stretching at least in onedirection to form microbeads of said cellulose acetate uniformlydistributed throughout said article and voids at least partiallybordering said microbeads on sides thereof in the direction(s) oforientation.
 2. The method according to claim 1 wherein said shapedarticle is selected from the group consisting of sheets, fibers and rodsand is oriented by stretching in one direction.
 3. The method accordingto claim 1 wherein said shaped article is a sheet and is oriented bystretching in two directions.
 4. The method according to claim 1 whereinsaid shaped article is a bottle and is biaxially oriented byblow-molding.
 5. The method according to claim 1 wherein said polyesteris poly(ethylene terephthalate).
 6. The method of forming a paper-likesheet comprising a continuous phase of polyester having dispersedtherein microbeads of cellulose acetate encircled by void spaces whenviewed in a direction perpendicular to the plane of the sheet, saidsheet when consisting only of said polyester continuous phase and saidmicrobeads at least partially bordered by void space characterized byhaving a Kubelka-Munk R value (infinite thickness) of about 0.90 toabout 1.0 and the following Kubelka-Munk values when formed into a 3 milthick film:Opacity -- about 0.78 to 1.0 SX -- 25 or less KX -- about0.001 to 0.2 T(i) -- about 0.02 to 1.0said method comprising (a) forminga molten mixture of poly(ethylene terephthalate) and cellulose acetate,wherein the cellulose acetate is uniformly dispersed through saidpoly(ethylene terephthalate); said poly(ethylene terephthalate) having aTg of about 80° C., and an I.V. of at least 0.55, said cellulose acetatehaving an acetyle content of about 28 to 44.8% by weight, a viscosity ofabout 0.01-90 seconds and a Tg of about 20° C. higher than the Tg ofsaid poly(ethylene terephthalate), (b) casting a film of said mixture,and (c) orienting said film by stretching to form microbeads of saidcellulose acetate uniformly distributed throughout said film andencircled by doughnut-shaped voids lying in planes generally parallel toopposite surfaces of said film.